SUMMARY / ABSTRACT Gay, bisexual, and other men who have sex with men (MSM) continue to be the group most heavily impacted by HIV in the United States, despite stability or decline in infections among other groups. Up to two-thirds of MSM acquire HIV from their main partner (i.e., male couples). Given the multitude of available HIV prevention options, HIV-negative and HIV-discordant male couples may experience anxiety and decisional conflict in determining which HIV prevention methods to use in their relationship. Moreover, uptake of different evidence- based preventive strategies (e.g., PrEP, nPEP, couples- and individual-level HIV/STI testing) remains subpar in these two groups of male couples, which inhibits the overarching goal to reduce HIV and STI incidence. Patient-centered decision aids (PtDAs) have been shown to reduce decisional conflict and increase uptake of preventative behaviors; however, there are no existing couples-based HIV prevention PtDAs to assist male couples in choosing and then using their selected strategy(ies). The overarching goal of this two-year, mixed method project is to develop and examine the to develop and examine the feasibility, acceptability, and preliminary efficacy of a tailored, web-based interactive PtDA to encourage a convenience sample of 45 at-risk male couples in new relationships to develop a prevention plan, and order and use their selected prevention strategies based on their plan. Method: All project activities will be web-based. First, semi-structured, individual qualitative interviews will be conducted with both partners of 45 male couples (n=90 men), who are in new relationships, to examine perceived barriers and facilitators of partners? decision-making processes to use prevention strategies in their relationship (Aim 1). Findings from Aim 1 will be combined and applied to the proposed outline, design, and experience of the PtDA with the web development company, consultant, and community advisory board (CAB). The CAB and investigative team will then test the prototype and alpha version of the PtDA before beginning Aim 2 with the beta version of it. With the use of a different convenience sample of 45 eligible male couples in new relationships (Aim 2), the feasibility, acceptability, and preliminary efficacy of the PtDA will be assessed to determine whether couples developed a prevention plan for uptake and/or continued use of their selected HIV preventive strategy(ies). Dyadic data will be captured via: 1) brief, quantitative, pre- and post-intervention assessments taken at baseline and 2 months; 2) selections made within the PtDA; 3) pictures provided by participants about use of strategies; 4) semi-structured individual, exit interviews conducted at 2 months. The sample ? for both aims ? will be stratified (e.g., race/ethnicity, couples? HIV-status). Significance: If acceptability of the HIV prevention PtDA is high and shows initial promise to improve uptake and use of evidence-based strategies, our findings will support follow-up with a R01 application to test the intervention efficacy in a fully powered randomized controlled trial with a larger diverse sample of at- risk male couples in new relationships throughout the U.S.